UVa 589 - Pushing Boxes

题目：二维推箱子游戏，给你箱子、人和目标的位置，输出问题的解（推箱子和行走的路径）。

分析：搜索、优先队列。优先顺序为：首先保证推箱子的字数最少、然后是走的步数最少。

利用二叉堆做优先队列，在上面进行bfs即可。

说明：注意搜索时按照字典序方向枚举，不然会WA╮(╯▽╰)╭。

#include <algorithm>
#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cstdio>
#include <cmath>

using namespace std;

char maps[20][21];

typedef struct node0
{
	int  X,Y,x,y;
	int  front,push,move,id;
	char step;
}dnode;
dnode H[160001];
dnode Q[160001];
bool  U[20][20][20][20];
int   dxy[4][2] = {0,1,-1,0,1,0,0,-1};
char  O[5] = "ENSW",o[5] = "ensw";
int   q_size;

//banery_heap define
int bh_size; 

void bh_init()
{
	bh_size = 0;
}

int bh_empty()
{
	return bh_size == 0;
}

bool bh_cmp(dnode a, dnode b)
{
	if (a.push != b.push)
		return a.push < b.push;
	return a.move < b.move;
}

void bh_insert(dnode s)
{
	H[++ bh_size] = s;
	int now = bh_size;
	while (now > 1 && bh_cmp(H[now], H[now>>1])) {
		swap(H[now], H[now>>1]);
		now = now>>1;
	}
}

dnode bh_delete(void)
{
	swap(H[bh_size], H[1]);
	int now = 1;
	while (1) {
		int New = now,L = (now<<1),R = (now<<1)+1;
		if (L < bh_size && bh_cmp(H[L], H[New])) New = L;
		if (R < bh_size && bh_cmp(H[R], H[New])) New = R;
		if (now == New) break;
		swap(H[now], H[New]);
		now = New;
	}
	return H[bh_size --];
}
//banery_heap end

void output(dnode s)
{
	if (s.front) {
		output(Q[s.front]);
		printf("%c",s.step);
	}else printf("%c",s.step);
}

void bfs(dnode s, int n, int m)
{
	memset(U, 0, sizeof(U));
	U[s.X][s.Y][s.x][s.y] = 1;
	q_size = 0;

	bh_init();
	bh_insert(s);

	while (!bh_empty()) {
		dnode New,now = bh_delete();
		Q[q_size ++] = now;
		for (int k = 0 ; k < 4 ; ++ k) {
			New = now;
			New.x += dxy[k][0];
			New.y += dxy[k][1];
			New.front = q_size-1;
			if (New.x < 0 || New.x >= n || New.y < 0 || New.y >= m)
				continue;
			//推箱子
			if (New.X == New.x && New.Y == New.y) {
				New.X += dxy[k][0];
				New.Y += dxy[k][1];
				if (New.X < 0 || New.X >= n || New.Y < 0 || New.Y >= m)
					continue;
				if (maps[New.X][New.Y] != '#' && !U[New.X][New.Y][New.x][New.y]) {
					New.step = O[k];
					New.push ++;
					if (maps[New.X][New.Y] == 'T') {
						output(New);
						return;
					}
					U[New.X][New.Y][New.x][New.y] = 1;
					bh_insert(New);
				}
			}else if (maps[New.x][New.y] != '#' && !U[New.X][New.Y][New.x][New.y]) {
				New.step = o[k];
				New.move ++;
				U[New.X][New.Y][New.x][New.y] = 1;
				bh_insert(New);
			}
		}
	}
	printf("Impossible.");
}

int main()
{
	int n,m,t = 1;
	while (~scanf("%d%d",&n,&m) && n && m) {
		for (int i = 0 ; i < n ; ++ i)
			scanf("%s",maps[i]);

		dnode s;
		for (int i = 0 ; i < n ; ++ i)
		for (int j = 0 ; j < m ; ++ j) {
			if (maps[i][j] == 'S') {
				s.x = i; s.y = j;
			}
			if (maps[i][j] == 'B') {
				s.X = i; s.Y = j;
			}
		}

		printf("Maze #%d\n",t ++);
		bfs(s, n, m);
		printf("\n\n");
	}
    return 0;
}